The basic terminal homing problem with conventional seekers is that they do not reliably home on the target centroid. All radar systems suffer from poor end-game performance because of poor antenna beam resolution, the inability to resolve target centroid location from the target backscatter signal and countermeasures susceptibility. Passive optical seekers are generally more accurate than radar seekers in clear air tactical environments. However, the typical passive seeker systems track the infra-red radiation of the target exhaust and guide on a point located in the plume, or at best, the hot tail pipe.
The magnitude of the passive seeker problem with respect to miss distance is illustrated in FIG. 1. For tail and head-on target encounters with passive optical homing missiles, plume tracking may yield high hit probabilities, but in the event of broad side or beam encounters, target hit probabilities are greatly reduced since the guidance homing point is on the plume or tail pipe of the target aircraft. Currently, passive seeker studies are under way to reduce the broad side miss distance distribution. The typical techniques involved are edge bias and lead bias concepts. Theoretically, edge bias will cause the seeker to track the tail pipe and lead bias can then be used to cause the missile-target contact point to occur at some predetermined distance in front of the passively tracked tail pipe.